This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A172087 #11 Apr 22 2021 12:36:51
%S A172087 1,1,3,3,15,15,21,21,15,15,33,33,1365,1365,3,3,255,255,399,399,165,
%T A172087 165,69,69,1365,1365,3,3,435,435,7161,7161,255,255,3,3,959595,959595,
%U A172087 3,3,6765,6765,903,903,345,345,141,141
%N A172087 A001897 with terms repeated.
%t A172087 b[n_] := -2*(2^(2*n - 1) - 1)*BernoulliB[2*n]; t = Table[b[n], {n, 0, 30}] // Denominator; A172087 = Transpose[{t, t}] // Flatten (* _Jean-François Alcover_, Jan 11 2016 *)
%Y A172087 Cf. A001897, A172087.
%K A172087 nonn
%O A172087 0,3
%A A172087 _Paul Curtz_, Jan 25 2010
%E A172087 More terms from _Jean-François Alcover_, Jan 11 2016
%E A172087 Edited by _N. J. A. Sloane_, Apr 22 2021.